Eating lots of animal protein appears to increase women's risk of developing inflammatory bowel disease (IBD), according to a new study from France.

"Our results may help better understand the role of diet in IBD risk," Dr. Franck Carbonnel of the Center Hospitalier Universitaire de Bicetre in Paris and his team write in the American Journal of Gastroenterology. "If confirmed, they can lead to protective strategies, especially in families at risk of IBD, and possibly to advice for preventing relapse."

Inflammatory bowel disease is a collective term for diseases characterized by severe inflammation in the digestive system such as ulcerative colitis, which typically only affects the colon, and Crohn's disease, which can attack the entire digestive tract. IBD, which affects about one in 500 people, has become much more common since World War II, Carbonnel and his colleagues note. The reasons behind the increase are still unclear.

To investigate whether diet might be a factor, the researchers followed more than 67,000 women participating in a long-term study of risk factors for cancer and other common illnesses. The women were 40 to 65 years old when they enrolled in the study.

During follow-up, which averaged about 10 years, just 77 of the women developed inflammatory bowel disease. Ninety percent of women in the current study were eating more than the recommended dietary allowance of protein.

Women who consumed the most protein were at more than triple the risk of being diagnosed with IBD, the researchers found; animal protein accounted for most of the risk. Risk was specifically associated with high intake of meat and fish, but not with dairy products or eggs.

While experts have long suspected that diet might play a role in inflammatory bowel disease, Carbonnel and his colleagues note, the only links identified previously were with eating a lot of fats and certain kinds of sugars. Those studies were more prone to error than forward-looking or prospective studies like the current investigation. There have also been several studies linking vitamin D deficiency to IBD.

Another recent prospective study found that a diet high in omega-3 fatty acids decreased inflammatory bowel disease risk, while eating lots of omega-6 fatty acids increased it, Carbonnel noted in an interview with Reuters Health. Omega-3s are found in fish oil, flax seed oil, and a few other sources; omega-6s, which Westerners tend to eat much more of, are found in several types of vegetable and nut oils.

Meat could contribute to inflammatory bowel disease risk because digestion of animal protein produces many potentially toxic "end products," such as hydrogen sulfide and ammonia, the researchers note. Also, Carbonnel pointed out, a high-protein diet could alter the mix of bacteria that live in the colon.

"These findings have to be confirmed in other populations, particularly in men and younger subjects," the researcher said, adding that if they are confirmed, the next step would be to conduct a trial comparing the effects of restricted versus unrestricted animal protein on inflammatory bowel disease risk.

Given the large amount of protein women in the study were eating, he added, a restricted diet wouldn't involve radically reducing protein intake, but instead sticking to the recommended amount.